Medical or dental handpiece with a rear and a front shaft section that form an obtuse angle

ABSTRACT

The invention relates to a medical or dental medical handpiece ( 3 ) having an elongate shaft ( 13 ), which has in its front end region a tool holder ( 5 ) having a lateral insertion opening ( 5   a ) for a tool ( 6 ), and having a rearward and a forward shaft section ( 13   a   , 13   b ) which include an obtuse angle (W 2 ) which is open to the side away from the insertion opening ( 5   a ), wherein in the shaft sections ( 13   a   , 13   b ) there is rotatably mounted in each case a drive shaft section ( 53   a   , 53   c ), which stand in driving connection with one another by means of gears meshing with one another, and wherein the forward shaft section ( 13   b ) stands in driving connection with the tool holder ( 5 ) by means of gears ( 58, 59 ) meshing with one another. In order to improve handling, the angle (W 3 ) include between the middle axis ( 16 ) of the insertion opening ( 5   a ) and the middle axis ( 13   e ) of the forward shaft section ( 13   b ) is greater than 90° and the forward gear ( 58 ) of the forward drive shaft section ( 53   c ) meshes on its side away from the insertion opening ( 5   a ) with the gear ( 59 ) of the tool holder ( 5 ).

This is the U.S. national phase of International Application No.PCT/EP02/08932 filed Aug. 9, 2002, the entire disclosure of which isincorporated herein by reference.

The invention relates to a medical or dental-medical handpiece accordingto the preamble of claim 1 or 5.

A medical or dental-medical handpiece is an object which is put to usefor working the human body or natural or artificial parts thereof, suchas prostheses, with a tool. The tool is in most configurations amaterial removing tool which acts on the body with a rotational movementor with a movement going back and forth. As drive there serves arotational motor which may be arranged in the handpiece itself or in aso-called connection part with which the handpiece is releasablyconnected by means of a plug-in, in particular a plug-in/turn couplinghaving a coupling recess in one the one part and a coupling pin,engaging the coupling recess, on the other part. Also in the presence ofa back and forth going tool drive, the drive movement is derived from arotary movement which at least one rotary part carries out and for thispurpose is rotatably mounted in the inner ring of a roller bearinghaving the inner ring and an outer ring. For axially positioning theinner ring and/or the outer ring of a roller bearing it is usual toprovide shoulder surfaces on which the roller bearing ring concernedbears and thus is restricted against an axial movement.

In the case of a dental medical handpiece described in DE 44 08 574 A1(see in particular FIGS. 1 and 2 of this document), the drive shaftsection rotatably mounted in the forward shaft section is drivinglyconnected with the tool holder by means of a herringbone geartransmission, which tool holder is formed by means of a receiving sleeverotatably mounted and extending transversely to the shaft, on which theassociated herringbone gear meshes with the herringbone gear on theforward drive shaft section on its side towards the insertion opening.The angle included between the middle axis of the tool holder and themiddle axis of the forward shaft section is about 90°. The forward driveshaft section and a non-illustrated rearward drive shaft section areconnected with one another by means of a herringbone gear transmission,the gears of which have teeth on their sides towards one another whichstand in engagement with one another.

From EP 0 185 400 B1 there can also be understood a handpiece asdescribed above, which in accordance with FIG. 2 has in the apex regionof an angling a drive shaft section which is connected in each case bymeans of a herringbone gear transmission with a rearward drive shaftsection and a forward drive shaft section, and which extends obliquelyfrom the rear forwardly between the rearward and the forward drive shaftsection.

In the publication DE 93 07 903 U1 there is described a dental medicalhandpiece having an angled handpiece shaft, in which there are rotatablymounted a rearward drive shaft section, a middle drive shaft section anda forward drive shaft section. The middle drive shaft section is, withregard to the rearward drive shaft section, arranged offset towards theside away from the tool, and it has at its forward end, which is locatedin the bend region of the handpiece, a hollow gear which meshes with arearward gear on the forward drive shaft section in such a manner thatthe latter meshes with the hollow gear of the middle drive shaft sectionon its side towards the tool.

With such a handpiece in which there is rotatably mounted, for the driveof the tool holder, a drive shaft of a plurality of drive shaft sectionsthere arise particular demands in particular in the region of the apexof a handpiece angled or curved to the side, taking into account desiredspeeds of rotation and/or directions of rotation, whereby here also acompact construction is to be striven for in order to obtain a simpleconstruction in the restricted space of a handpiece.

The invention thus has the object of improving a medical or dentalmedical handpiece with regard to the effectiveness of the drive shaftsections standing in driving connection with one another.

With a configuration in accordance with one embodiment of the invention,the rear gear of the forward drive shaft section on its side away fromthe insertion opening for the tool meshes with the gear of the rearwarddrive shaft section on the side towards the insertion opening. Thisconfiguration leads not only to a simple and robust construction, but itmakes possible in comparison with known drive connections a reversal ofdirection of rotation, which may be desired for various reasons. Forexample, a further middle drive shaft section may be provided whichmakes it possible to reverse the direction of rotation of the forwarddrive shaft section and/or to bring about stepping up of the speed ofrotation or stepping down of the speed of rotation. Through this, thehandpiece can be so altered that it can fulfill specific or a largerange of demands and thus the range of applications of the handpiece canbe increased.

A medical or dental-medical handpiece according to another embodiment ofthe invention is described in U.S. Pat. No. 4,278,428 A. Here there isinvolved a dental drill handpiece of curved form with a tool which canbe inserted from the side, whereby there extends in the shaft of thehandpiece a drive train of a plurality of the drive shaft sections. Arearward drive shaft section, extending up to the beginning region ofthe curvature, and a forward drive shaft section extending therefromforwardly, stand in engagement with one another by means of a geartransmission, whereby the rearward gear of the forward drive shaftsection meshes, on its side away from the tool, with the associated gearof the rearward drive shaft section (see exemplary embodiment accordingto FIG. 10).

In the case of a handpiece for or with a tool which in functionaloperation rotates at high speed, improvement is needed with regard tothe noise caused thereby, to the effect that the running noise isreduced or avoided, since a noisy operation is disturbing both for theperson carrying out the treatment and also for the patient. This appliesin particular for handpieces which are used in the head region of thepatient as is the case with dental medical handpieces.

The invention thus also has the object of so configuring a medical ordental medical handpiece that a low noise operation and/or a simple andstable construction is attained.

A handpiece in accordance with this embodiment of the invention has, formounting the tool holder, a roller bearing with at least two roller bodyrows arranged next to one another, which are located to both sides ofthe forward gear of the drive shaft, whereby the latter or the geararranged thereon radially passes through the outer sleeve of the rollerbearing in a through-hole.

A configuration in accordance with this embodiment of the inventionleads to a reduction of the running noise. This can be attributed to thefact that a common roller bearing outer sleeve is present which makespossible a stabilised support in the head of the handpiece, which leadsto a reduction of the running noise. Thus, this configuration inaccordance with the invention is in particular suitable for a handpiecefor or with a tool which rotates at high speed in functional operation,as is the case with high speed motor handpieces or turbine handpieces.This configuration in accordance with the invention is suitable,however, also for low speed handpieces, whereby the otherabove-mentioned advantages can be attained.

Through this configuration, the construction is simplified, because onlyone roller bearing is needed for mounting the tool holder. Through thisnot only is the number of necessary individual components reduced, butalso the effort needed for installation or de-installation, since onlyone roller bearing needs to be installed or de-installed.

With regard to its readiness of handling at the site of treatment, highdemands are made of a handpiece of the kind concerned here. This becausein many cases there is to be carried out work which is on the one handfine and on the other hand precise. Here, for ergonomic reasons, thereare to be striven for a handling-friendly construction of the handpieceand a handling-friendly position of the handpiece during the treatmentor operation, so that the operating person can direct their attentionless to the handpiece and more to the site of operation.

Through further development of the handpiece it has been striven for toimprove its handling. This is achieved by means of another embodiment ofthe invention.

With this embodiment, the middle axis of the forward shaft section andthe middle axis of the insertion opening include an angle which isgreater than 90° and which is open towards the tool side of thehandpiece. Further, the gear arranged at the forward end of the forwarddrive shaft section meshes on its side away from the tool side of thehandpiece with the corresponding gear of the tool holder. Through thisthe handpiece is given a structural form which makes possible anergonomically favourable holding of the handpiece with the operatinghand, and thus places the operating person in the position of directingtheir attention less to the manual grasping of the handpiece and more tothe treatment or operational procedures. The configuration in accordancewith the invention is particularly suitable for a dental medicalhandpiece, because it is better adapted to the anatomy in the mouthregion of the patient and improves the moveability and exploitation ofspace in the mouth of the patient: In this regard, the invention isbased on the insight that the human upper and lower jaws in each casecan be opened with an angle of about 20°. In this respect, theconfiguration in accordance with the invention represents a median form,which makes it possible to move the handpiece in the free space presentbetween the jaws to both sides.

This further development leads to a simple and structurally favourableconstruction, which is suitable both for a so-called angled handpieceand also for a handpiece curved to the side in the forward region,whereby it is to be taken into account that in particular for a dentalmedical handpiece the structural size is restricted and therefore acompact structure is striven for, which the configuration in accordancewith the invention makes possible.

In comparison with the generic configuration indicated in theintroduction, the configuration in accordance with the invention leadsto a reversal of direction of rotation for the tool holder or the tool,whereby the reversal of direction of rotation is compensated and thus adrive can be used which is unchanged with regard to the direction ofrotation.

The configuration in accordance with the invention is suitable both fora rearward and a forward drive shaft section and also for an additionalmiddle or third drive shaft section which with respect to the middleaxis of the rearward drive shaft section may extend parallel orobliquely thereof.

Further features of the subclaims make possible a favourable mountingarrangement, which both simplifies the construction of the mounting andalso the installation of de-installation thereof and beyond this is ofcompact construction, which can be favourably arranged in the handpiece.

Further features of the subclaims make possible a simple, compact andeconomically producible construction, which is suitable in particularfor the restricted space conditions in a handpiece of the kind concernedhere. Further, there is made possible an axially effective securing fora roller bearing and a simple installation or de-installation of variouscomponents of the handpiece, in particular of the roller bearing and/orof drive shaft sections.

Below, advantageous configurations of the invention will be described inmore detail with reference to exemplary embodiments and drawings.

There is shown:

FIG. 1 a handpiece in accordance with the invention, in a side view,which together with a so-called connection part forms a treatmentinstrument;

FIG. 2 a handpiece in accordance with the invention, in further modifiedconfiguration, in axial section;

FIG. 3 the middle region, designated by Y, of the handpiece according toFIG. 2, in axial section to an enlarged scale.

FIG. 4 the forward end region of the handpiece, in longitudinal section,in a modified configuration.

The treatment instrument, designated in its entirety by 1 in FIG. 1,consists of a rearward instrument part, namely a so-called connectionpart 2, and a forward instrument part, namely the so-called handpiece 3,which are releasably connected with one another by means of a coupling4, in particular a plug-in coupling, preferably a plug-in/turn coupling.With the present exemplary embodiment there is arranged at the forwardend of the treatment instrument 1 a holder device 5 having a lateralinsertion opening 5 a for a tool 6, whereby the tool 6 may stand out tothe side or forwardly. The handpiece may extend straight (notillustrated) or curved (indicated by chain lines) to the side away fromthe tool 6, or angle shaped. The plug-in/turn coupling is formed bymeans of a coupling recess 7, round in cross-section, and in couplingpin 8 which can be inserted therein with slight play for movement. Withthe present exemplary embodiment, the coupling recess 7 is arranged atthe rearward end of the handpiece 3, and the substantially cylindricalcoupling pin 8 extends from the connection part 2 forwardly. In thecoupled condition the coupling recess 7 and the coupling pin 8 arereleasably latched to one another by means of a latching device 9. Thishas a latching element 9 a which is mounted radially moveably in the onecoupling part and is biassed by means of a spring force into a latchingposition, crossing the dividing gap, in which the latching element 9 aengages into a ring groove in the other coupling part. Such a latchingdevice 9 is self-actingly latched upon coupling and upon uncoupling canbe overcome by a manual exercise of an axial pulling force, whereby thelatching element 9 a is self-actingly forced into its release position.

The connection part 2 is connected with a flexible supply line 2 a,which is connected with a non-illustrated control apparatus. Thehandpiece 3 is preferably freely rotatably mounted on the coupling pin8, through which handling is improved. Through the plug-in/turn coupling4 there extends at least one media line 11 for a treatment or drivemedium, e.g. water, compressed air, or a water/air mixture (spray). Themedia line 11 can extend axially through a radial dividing gap (notillustrated) or Z-shaped through a hollow cylindrical dividing gapbetween the coupling recess 7 and the coupling pin 8, whereby the medialine 11 crosses the dividing gap in the region of a ring groove in thecoupling pin 8 or in the coupling recess 7, so that in any rotaryposition the passage of media is ensured. To both sides of the passage,the dividing gap is sealed by means of a sealing ring 8 a which may bearranged in a ring groove in the wall of the coupling recess 7 or in theouter surface of the coupling pin 8. Through this a free rotatabilitythrough 360° and more is ensured. The media line 11 extends from therearward end of the treatment instrument 1 to its forward end region,whereby it may run partially as a channel in the instrument body or as atube or pipeline. The media line 11 opens out in the forward end regionof the treatment instrument 1, out of this, whereby the outlet opening11 a is directed towards the treatment site or to the tip of the tool 6.

With all exemplary embodiments of the invention, for which the same orsimilar parts are provided with the same reference signs, the handpiece3 has a rotary part 12 mounted rotatably therein in a roller bearing.With the exemplary embodiment according to FIG. 1 there is involved onewith an arc-shaped curved (FIG. 1) or angled (FIG. 2) shaft 13. This canbe formed in one piece or consist of a rearward and a forward shaftsection 13 a, 13 b, which are fixedly connected with one another at thebeginning of the arc or at the apex of the angle. At the forward end ofthe shaft 13 there is located a thickened head 14 in which a receivingsleeve 18 is rotatably mounted, in which sleeve the tool 6 can beinserted with its shaft and can be releasably fixed in a manner knownper se by means of a fixing device.

In the case of this treatment instrument 1, a drive motor 51, forexample an electric motor, is arranged in the extended connection part2, indicated by chain lines, and drivingly connected with the receivingsleeve 18 by means of a drive shaft or drive shaft train 53 having aplurality of drive shaft sections. In the region of the plug-in coupling4 the drive shaft train 53 has a plug-in coupling 52 with two plug-incoupling elements 52 a, 52 b corresponding with one another in aform-fitting manner, whereby upon coupling and decoupling of the plug-incoupling 4 at the same time a coupling and decoupling of the plug-incoupling 52 is possible.

A drive shaft section 53 a arranged in the rearward end region of thehandpiece 3 extends up into the initial region of the curvature (FIG. 1)or the apex region of the angled (FIG. 3) shaft 13, whereby its forwardend is connected with a third drive shaft section 53 c by means of asecond drive shaft section 53 b extending, for example axially, insubstance only in the curvature or involute or in the apex region, whichthird drive shaft section extends in the forward shaft section 13 b upto the receiving sleeve 18 and is drivingly connected therewith. Forconnecting the drive shaft sections 53 a, 53 b, 53 c there is providedin each case a gear transmission. At the forward end of the first driveshaft section 53 a there is arranged a gear 54 having an internaltoothing, which meshes with a pinion 55 at the rearward end of thesecond drive shaft section 53 b. Thereby, the second drive shaft section53 b is arranged, with regard to the apex 13 c, the angling orcurvature, offset towards the side away from the tool 6, whereby on theforward end of the second drive shaft section 53 b and on the rearwardend of the third drive shaft section 53 c there is arranged in each casea pinion 56, 57 in substance in a transverse plane or overlapping oneanother, in the sense of spur or conical gears which mesh with oneanother. The second and the third drive shaft section 53 b, 53 c includean obtuse angle W1, which is open towards the side away from the tool 6.The angle W2, which is included by the forward end region of the forwardshaft section 13 b and its rearward end region or the rearward shaftsection 13 a, is likewise obtuse.

The drive connection between the third drive shaft section 53 c and thereceiving sleeve 18 is formed by means of an angled gear transmissionhaving a conical gear 58 at the forward end of the third drive shaftsection 53 c and conical gear 59 on the receiving sleeve 18. The toothengagement between the conical gears 58, 59 is, with reference to thethird drive shaft section 53 c, arranged on its side away from the tool6. Through this, the receiving sleeve 18 is driven in the same directionof rotation as the first drive shaft section 53 a. The receiving sleeve18 is rotatably mounted by means of two roller bearings 61, 62 (FIG. 2)in the head 14, which have a spacing from one another directedlongitudinally of the axis of rotation 16, which spacing is larger thanthe conical gear 58, so that the latter can be arranged therebetween,including the conical gear 59, which is arranged on the side of theconical gear 58 away from the tool 6 and at the same time on the side ofthe roller bearing 61 towards the tool 6, and which is arranged furtherdistant from the tool 6 than the other roller bearing 62. For rotarymounting of the second drive shaft section 53 c there is arranged ineach case a roller bearing 63, 64 (FIG. 2) on the end regions of thisdrive shaft section 53 c, the outer rings of which are seated andmounted in a non-illustrated longitudinal hole of the shaft section 13b.

The configuration of the gear 54 as a hollow gear makes possible withradially small manner of construction, a relatively great gearing up ofthe speed of rotation between the first and the second drive shaftsection 53 a, 53 b.

With the exemplary embodiment according to FIGS. 2 and 3 there areprovided for mounting the first drive shaft section 53 a and the seconddrive shaft section 53 b in each case in the shaft 13, a two-row rollerbearing 65, 66 in a bearing bush. This roller bearing 65, 66 issufficient in each case to mount the entire drive shaft section 53 a or53 b sufficiently stably. The first drive shaft section 53 a projectsbeyond the roller bearing 65 freely outstanding rearwardly, whereby aslight radial flexibility is present for coupling with the drive shaftsection 53 d of the connection part 2. For increasing the flexibilitythere may be connected between the first drive shaft section 53 a andgear 54 a joint connection 68 having a transverse pin 69, whereby theradial flexibility of the first drive shaft section 53 a is increased.The gear 54 consists of a rearward cylindrical or hollow cylindricalmounting section 54 a at the forward end of which a flange 54 b isarranged which carries at its forward side a hollow gear crown 54.

The roller bearings 65, 66 may have two roller bearing inner rings 65 b,66 b for example having an axial spacing from one another, or also oneaxially through-going roller bearing inner sleeve (not illustrated).

With the roller bearings 65, 66 the axial spacing of the roller rowsfrom one another can be advantageously greater than the mean diameter ofthe roller body raceways. The roller bearing 66 is so long, see L, thatit fits between the pinions 55, 56, whereby at the same time an axialrestriction is constituted for the second drive shaft section 52 b.

Both roller bearings 65, 66 are preferably mounted in a common carrierbody 71 forming a bearing bush 23, which sits in the shaft 13 in theregion of the rearward shaft section 13 a neighbouring the apex point,is mountable from the rear and again dismountable from the rear, or viceversa, through a rearwardly or forwardly opening receiving hole 71 a,and is axially fixable in the shaft section 13 a.

For axial securing or positioning, there is associated with the rollerbearing 66 in the bearing bush 23 a securing device 20 with at least onesecuring ring 24 of elastically deformable or elastically compressiblematerial, which is arranged so deep in a ring groove 25 in the innersurface 23 a of the bearing sleeve 23 that it projects beyond the innersurface 23 a and thus forms a securing bead with which it sits in a ringgroove 26, lying radially opposite to the ring groove 25, in the outersurface 66 c of the roller bearing outer ring 66 a. Preferably, thesecuring ring 24 presses with a, for example small, elastic biassingradially inwards against the base of the ring groove 26. This can beattained in that the inner diameter of the securing ring 24 is smallerthan the inner diameter of the ring groove 26 and/or in that the halfdifference between the inner diameter of the ring groove 26 and theouter diameter of the ring groove 25 is somewhat smaller than thediameter of the securing ring 24, which is preferably round incross-section. In both cases, the securing ring 24 is elasticallybiassed inwardly against the base of the ring groove 26. For improvingthe axial positioning it is also advantageous if the axial width of thering grooves 25, 26 is somewhat smaller than the axial dimension of thesecuring ring 24, so that this is elastically compressed between theside walls or flanks 26 a of the ring groove 25, 26. In the case of theexemplary embodiment, the cross-sectional form of the ring groove 25 isquadrilateral, and the cross-sectional form of the ring groove 26 isrounded in the form of a circular arc section. Other cross-sectionalforms are however also possible.

For facilitating installation, the roller bearing 66 has at least on oneend face a rounded or acute angled lead-in surface 27, which upon axialpushing in of the roller bearing 66 into the bearing bush 23self-actingly elastically deforms and stretches the securing ring 24 andself-actingly springs this again into the ring groove 26 in theinstalled position. Preferably, a lead in surface 27 is provided at bothend faces.

It is further advantageous to arrange the ring groove 26 axially offsetwith regard to the races of the roller bodies 22, through which materialweakening of the roller bearing outer ring 66 a is of lesser, orwithout, effect. Preferably the roller bearings 66 are similarly formed,so that the roller bearing 66 selectively fits to the one or to theother bearing position, e.g. in a position rotated by 180°.

If an axial securing of the roller bearing 66 is desired only in oneaxial direction, the ring groove 26 can be formed to run out axially toone side, as is shown per se by the exemplary embodiment according toFIG. 3 which is still to be described. With such a configuration, theflanks 26 a of the ring groove 26 towards one another are adapted to theaxial spacing of the securing rings 24 present and this preferably suchthat the securing rings 24 press with an elastic tension or compressionagainst the preferably convergent flanks 26 a.

As FIGS. 2 and 3 allow further to be recognised, in order to achieve anaxially effective yieldability for the securing device 20 it isadvantageous to arrange the associated roller bearing 66 in each case atan axial spacing from associated components of the head housing, so thatthe above-described axial yieldability is not restricted. If the axialyieldability is desired in only one axis direction, the roller bearingring concerned can be restricted in the other axial direction by meansof a bearing surface.

In the case of the exemplary embodiment, there are arranged two ringgrooves 25, in each case with a securing ring 24, in the bearing bush23, which for example are inwardly offset with reference to the rollerbearing races.

As can be further understood from FIGS. 2 and 3, the rearward rollerbearing 65 is in inserted from the rear into the receiving hole 71 a ofthe carrier body 71 and for example by means of a flange 65 b arrangedat the rearward end of the outer bearing sleeve 65 a axially fixedtowards the fore. The forward roller bearing 66 is, in contrast, placedfrom the fore into a receiving hole 72 of the carrier body 71 andaxially fixed or positioned by means of a securing device 20 with one ortwo securing rings 24. The flange forming the gear 54 is mounted in thereceiving hole 71 a between the roller bearing 65 and the bottom of thereceiving hole 71 a with play for movement. The outer ring 65 a may beset up, by means of a securing device, corresponding to the securingdevice 20 according to FIG. 3 and rotated by 180°, against an unintendeddisplacement to the rear, which is not illustrated in FIGS. 2 and 3.

With the configuration according to FIG. 3, however, the followingspecial feature may be provided. On the one hand, the roller bearingouter ring, here the common outer mounting sleeve 66 a, is positioned atone of its ends, here at its rearward end, at a shoulder 67 in thebearing bush 23, which shoulder may be formed by means of a step surfacein the bore receiving the outer bearing sleeve 66 a. Further, the atleast one ring groove 26 is, upon abutment of the outer bearing sleeve66 a on the shoulder 67, offset towards the axial direction away fromthe shoulder 67, with regard to the associated ring groove 25, which canbe clearly seen from FIG. 3. Through this offset, the securing ring 24is non-symmetrically deformed with regard to its ring plane, whereby dueto its elasticity its seeks to take its symmetrical form. Through thisthe securing ring 24 generates an axial force, see arrow 68, whichelastically biasses the outer bearing sleeve 66 a against the shoulder67 and thus ensures its bearing on the shoulder 67.

A further advantage of the securing or positioning device 20 consists inthat through the securing ring 24 a ring seal for the sealing off of thegap between the inner surface 23 a and the bearing pin is formed, and inparticular then when the securing ring 24 is elastically biassed notonly against the bottom of the ring groove 26 but also against thebottom the ring groove 25.

81 designates a light conductor rod, which extends in the vicinity ofthe edge of the tool side of the shaft 13 in the shaft from the rearforwardly to the outlet window 82 directed towards the free end of thetool 6. In functional operation of this handpiece 3 light is coupled infrom a light source 83 into the light conducting rod 81, whereby thelight source 83 is arranged on a carousel 84 (schematically illustrated)rotatably mounted in or on connection part 2, which carousel isform-fittingly connected with the handpiece 13 by means of a carrier 13d, so that also in this case the free rotatability of the handpiece 3 inthe plug-in/turn coupling 4 is ensured. The light conductor rod 81and/or other media lines may run in an outwardly open longitudinalgroove 73 in the carrier body 71. There may be arranged a plurality oflongitudinal grooves 73 offset with respect to one another in thecircumferential direction. In the region of the at least onelongitudinal groove 73 the may be arranged in each case a longitudinalgroove also in the flange 65 c.

The securing device 20 in accordance with the invention may also bearranged between the inner ring 65 b or 66 b and the rotation part 12concerned in a configuration corresponding to the above-describedconfigurations.

The angle W3 included in FIGS. 1 and 2 between the middle axis of theforward shaft section 13 b and the axis of rotation 16 of the receivingsleeve 18 is more than 90°, preferably substantially 100. Such aconfiguration is particularly favourable taking into account the anatomyin the mouth of a patient.

The rod-like handpiece 3 forms a grip part with the rearward grip orshaft section 13 a, which preferably extends straight, and the forwardgrip or shaft section 13 b adjoining thereon forwardly, which inaccordance with FIG. 1 develops curved towards the side away from theinsertion opening 5 a. The curvature may be even, in particular in theform of a section of a circular arc, or may be formed to be digressivein the direction forwardly, i.e. the shaft section 13 b may be morestrongly curved in its rearward region than its forward region. Theangular range W4 in which the curvature develops, may be about 10° to28° in particular about 19°. The outer curvature radius r may be about145 mm to 175 mm, in particular about 160 mm. The length of the curvedshaft section 13 b may be about the half of the overall length of theshaft 13. The middle axis 16 of the holder device 5 includes with thesection of the curved middle axis 13 e extending rearwardly from theintersection point, or with a tangent T touching the curved middle axis13 e at the intersection point, the angle W3. The intersection pointbetween the middle axes 5 a and 13 e may lie at the forward end of theangle range W4 or may have an axial spacing x form the angle range W4.

The forward shaft section 13 b may taper continuously forwardly, therebyuniformly or non-uniformly, e.g. digressively, so that itscross-sectional dimension y may be about 9 mm in the forward end region.In the rearward region of the forward shaft section 13 b, thecorresponding cross-sectional dimension z may be in substance 15.2 mm.

At least the forward shaft section 13 b is constituted at its surface tobe rough, to increase its gripability. For this purpose there may servea microstructure 86 not illustrated in detail, the roughness depth ofwhich is about 3 μm to 15 μm, preferably about 6 μm. The rough surfacemay be worked directly into the surface of the shaft section 13 b,preferably of metal, e.g. corrosion resistant steel, in particularnickel silver, or it can be worked into the surface of a coating of theshaft section 13 b.

In the above-described manner, also the shaft 13 overall may beconstituted to be rough.

The shaft 13, with its sections 13 a, 13 b, may be constituted in onepiece or two pieces. In the case of a two-piece configuration, the shaftsections 13 a, 13 b may be connected releasably, for example screwedtogether, with one another or non-releasably connected with one another.

With the exemplary embodiment according to FIG. 4, the receiving sleeve18 in the head 14 is mounted in a two-row roller bearing 91, which has athrough-going outer bearing sleeve 91 a and two inner bearing sleeves 91b arranged at an axial spacing from one another. The forward drive shaftsection 53 c, with its forward conical gear 58, engages through theouter bearing sleeve 91 a in a radial through-hole 92, and it mesheswith the conical gear 59 arranged within the outer bearing sleeve 91 aand between the inner bearing rings 91 b. The latter conical gear ispreferably arranged offset towards the side away from the insertionopening 5 a so that it meshes with the conical gear 58 on its side awayfrom the insertion opening 5 a. In the case of the exemplary embodiment,the conical gear 59 is arranged, for example formed in one piece, on anend thickening 18 a of the receiving sleeve 18. On the thickening 18 a,which is formed at least in sections to be outwardly cylindrical, theinner bearing ring 91 b of the associated roller body row can be mountedand preferably bear on a flange 18 b of the thickening 18 a with its endtowards the insertion opening 5 a, on which flange of the thickeningthere may also be formed the teeth on the side away from the innerbearing ring 19 b. Between the middle axis 16 and the middle axis 13 eor the tangent T, there is included the angle W3. The angle W3 may,however, also be about 90°, as is illustrated in FIG. 4. Within thescope of the invention it is also possible to arrange the conical gear59 offset to the insertion hole 5 a, so that it meshes with the conicalgear 58 on its side towards the insertion opening 5 a, which is notillustrated. The above-described variants with regard to the angle W3and the position of the conical gear 59 may also alternatively bepresent in the case of the exemplary embodiments according to FIGS. 1and 2.

In the case of the exemplary embodiment according to FIG. 4, there isarranged in the receiving sleeve 18, in its region towards the insertionopening 5 a, a per se known clamping sleeve 18 c having mutuallyopposite lying jaws 18 d for the shaft of the tool 5. For releasing thetool 5, a release device 93 is arranged on the side away from theinsertion opening 5 a, having a release pin 93 a which is axiallydisplaceably mounted in the receiving sleeve 18 and can be pushed with awedge 93 b between the clamping jaws 18 d. For actuation of the releasepin 93 a there is provided a push button 93 c, which can be pushed inagainst the force of a compression spring 94 arranged covered by meansof a flange of the push button 93 c. The release device 93 with the pushbutton 93 c is arranged on a screw flange 95 which with a hollowcylindrical screw ring 95 a can be screwed into a threaded hole of thehead 14 and covers over a receiving hole 96 in which the outer bearingring 91 a is correspondingly pushed in from the side away from theinsertion opening 5 a and with its end towards the insertion opening 5 abears on an inner shoulder 14 a of the head 14, and is thus axiallybounded between the latter and the screw flange 95.

On the tool side of the head 14 there is screwed into the head 14 ascrew flange 97 surrounding the receiving sleeve 18, which screw flangehas one or more channels 98 arranged distributed around thecircumference and directed at the treatment site, which channels startfrom a ring groove 99 in the head 14, which ring groove is connectedwith the media line 11. For sealing the ring groove 99 twoconcentrically arranged O-rings 101, 102 are arranged between the screwflange 97 and the head housing, in ring grooves which are preferablyformed in the screw flange 97.

For securing the through-hole 92 in its position, there is provided forthe outer bearing ring 91 a a rotational securing means 103, which ispreferably form-fittingly effective. In the case of the exemplaryembodiment, the rotational securing means 103 is formed by means of anannex 103 a on the circumference of the bearing outer ring 91 a and arecess 104 in the wall of the head 14 which receives this annex. Therecess 104 is formed as a slit running out towards the side away fromthe insertion opening 5 a, so that the outer bearing sleeve 91 a can bepushed in.

For its stabilisation, between the roller bearing rows the rollerbearing outer ring 91 a is preferably inwardly thickened.

1. Medical or dental medical handpiece having an elongate shaft, whichhas in a forward end region thereof a tool holder having a lateralinsertion opening for a tool, and having a rearward shaft section and aforward shaft section which include an obtuse angle which is open to aside away from the insertion opening, in the shaft sections there beingrotatably mounted in each case a drive shaft section, each of whichstands in driving connection with one another by means of gears meshingwith one another, and the forward shaft section standing in drivingconnection with the tool holder by means of gears meshing with oneanother, between the rearward drive shaft section and the forward driveshaft section there being arranged a middle drive shaft section, offsettowards a side away from the insertion opening, a rearward gear of whichmeshes with a hollow gear crown of a forward gear of the rearward driveshaft section, the middle drive shaft being mounted in a roller bearing,a bearing bush disposed in the rearward shaft section, the bearing bushadapted to axially receive the roller bearing, and a securing devicedisposed on an inner surface of the bearing bush, the securing devicepositioning and securing the roller bearing within the bearing bush, theforward drive shaft section and the middle drive shaft section standingin driving connection with one another by means of pinion gears, whereinthe pinion gears are in the form of spur or conical gears and therearward gear of the forward drive shaft section, on its side away fromthe insertion opening, meshes with an associated gear of the middledrive shaft section, and the securing device comprises a securing ring.2. Medical or dental medical handpiece according to claim 1, wherein theangle included between a middle axis of the insertion opening and amiddle axis of the forward shaft section is greater than 90° and theforward gear of the forward drive shaft section meshes on its side awayfrom the insertion opening with the gear of the tool holder. 3.Handpiece according to claim 1, wherein the forward shaft section iscurved in an arc-shape towards the side away from the insertion opening.4. Handpiece according to claim 3, wherein the curvature commences inthe region of the middle drive shaft section or of the apex. 5.Handpiece according to claim 1, wherein the securing ring comprises anelastically deformable material.
 6. Handpiece according to claim 1,wherein the inner surface of the bearing bush includes a ring grooveadapted to at least partially receive the securing ring.
 7. Handpieceaccording to claim 6, wherein a portion of the securing ring projectsbeyond the inner surface of the bearing bush, the portion forming asecuring bead.
 8. Handpiece according to claim 7, wherein an outersurface of the roller bearing includes a bead groove adapted to receivethe securing bead.